1. Field of the Invention
This invention relates to a composition for forming zinc oxide-based films on various substrates, a process for producing a zinc oxide-based film, said process making use of the composition, and a zinc compound suitably usable in the composition.
2. Description of Related Art
Concerning zinc oxide-based films, a variety of studies are under way for applications as electrically conductive (hereinafter referred to simply as “conductive”) transparent films, electrode materials, and semiconductor materials. Reported as processes for forming a zinc oxide-based film by using a zinc-oxide precursor compound include vapor-phase processes, such as CVD process and ALD process, that bring vaporized gas of a precursor compound into contact with a substrate (base material); and liquid-phase processes, such as MOD process and sol-gel process, that bring a solution or dispersion of a precursor compound into contact with a substrate.
Zinc compounds useful as zinc-oxide precursor compounds in these processes include alkoxides, β-diketone complexes, organic acid metal salts, zinc alkyls, inorganic salts, and the like. These precursor compounds are converted into zinc oxide through reactions under heat and/or with oxidizing agents.
For example, Patent Document 1 discloses a process for producing a thin zinc oxide film, which comprises bringing a suspension, in which a powder or fine particles of a zinc compound is or are dispersed, into contact with a surface of a substrate, and then thermally decomposing the zinc compound to convert the same into zinc oxide. As such zinc compounds, zinc acetate, zinc acetylacetonate, zinc oxalate, and zinc lactate are disclosed.
Patent Document 2, on the other hand, discloses a method for producing a transparent conductive film by bringing gas of an organic metal compound, said gas having been brought into a plasma state, into contact with a substrate under atmospheric pressure or a pressure around atmospheric pressure. In Patent Document 2, zinc oxide is exemplified as a transparent conductive film, and ethyl acetoacetate is exemplified as a ligand for forming an organic metal. Further, zinc acetylacetonate is exemplified as a zinc compound.
When forming a zinc oxide-based film by using a precursor compound, a temperature that is needed to convert the precursor compound into a zinc oxide-based film of quality sufficient to exhibit an expected function is generally considered to be 350° C. or higher. It is, however, desired to permit the conversion into such a zinc oxide-based film at a lower temperature from the standpoint of the adaptability to a resin substrate, a reduction in damage to a substrate, and the like. There is, accordingly, an outstanding desire for the development of a processor method for producing a zinc oxide-based film at a lower film-forming temperature than before.